A polymer alloy comprising a polyamide and a polyphenylene ether can become a very useful material by being incorporated with an elastomer, and conventionally has been applied to various uses.
For example, Japanese Patent Application Laid-Open No. 61-204262 discloses a composition comprising polyamide, polyphenylene ether and a styrene type hydrocarbon polymer block-conjugated diene type elastomer block copolymer. Further, Japanese Patent Application Laid-Open Nos. 62-129350, 2-135246 and 5-339496 disclose that a rubbery polymer composition containing polyphenylene ether, polyamide, an ethylene-α-olefin copolymer and the like has improved impact resistance.
However, the above prior art has been effective at improving the impact strength of compositions, but there is a big problem that a continuous phase of the polyamide absorbs water from the air resulting in a great size change of the molded piece.
In recent days, there has been an increasing demand for electroconductive materials, especially integrated circuit tray materials and electrostatically painted external trim parts for automobiles and motorcycles. Namely, they have been required to have high electroconductivity in addition to impact resistance, surface smoothness and small dimensional changes after water absorption.
As prior art relating to electroconductive resin compositions, Japanese Patent Application Laid-Open No. 8-48869 discloses that an electroconductive resin composition having a low melt viscosity and high impact resistance can be obtained by incorporating an electroconductive carbon black into a compatibilized polyphenylene etherbase resin. Further, Japanese Patent Application Laid-Open No. 10-310695 discloses an electroconductive composition comprising polyethylene ether, an impact modifying polymer containing ethylenically unsaturated structural units in a specific amount or more, various polyamides and an electroconductive carbon black.
However, the electroconductivity values in the above prior documents are measured between fractured surfaces of a broken off molded piece. In other words, it is measured by totally ignoring influences of the skin layer of the molded piece. Generally, such a process for charging a molded article wherein the molded article is broken off and then a voltage is applied thereto is not actually practical. The electroconductivity measured according to such a method is not practical at all. Moreover, the compositions obtained by the prior art are less worth using because of their inferior appearance (surface smoothness).
In general, the electroconductivity and the surface smoothness are contradictory properties. Namely, materials having higher surface smoothness tend to have inferior electroconductivity.
The electroconductivity is measured by applying a silver paste to two faces facing each other and measuring a resistance value therebetween. Accordingly, materials having higher surface smoothness have a lower contact area with the silver paste so that the resistance value of the materials tend to be higher.
However, there has been demanded materials exhibiting high electroconductivity without deteriorating impact resistance, surface smoothness and the small dimensional changes after water absorption, wherein the electroconductivity is measured without breaking off a molded piece.
On the other hand, Japanese Patent Application Laid-Open No. 2-201811 discloses a resin composition comprising polyphenylene ether, polyamide and an electroconductive carbon black wherein the electroconductive carbon black is introduced mainly in the polyamide, and it teaches that the electroconductivity (surface resistivity) is achieved by a method wherein a piece is not broken off from a molded article. However, according to this prior art, properties important to the composition (impact resistance, surface smoothness and small dimensional changes after water absorption) are greatly deteriorated so that the resultant composition is less worth using.
As described above, none of prior art has completely satisfied market demands for a composition having excellent impact resistance and surface smoothness and displaying only small dimensional changes after water absorption. In addition, it has been very difficult to impart to compositions high electroconductivity which can be achieved by a method wherein a piece is not broken off from a molded article.